kcal scanner: kilojoules, kilocalories and metric labels

kJ, kcal and the word "calorie"

Three units are in play and two of them are the same thing.

A kilocalorie (kcal) is the energy needed to raise one kilogram of water by one degree Celsius. When a label, a diet plan or a person says "calories", they mean kilocalories. The lower-case "calorie" is technically a thousand times smaller, and essentially nobody uses it in a food context — which is why "a 2,000 calorie diet" and "2,000 kcal" mean the same thing despite appearing to differ by a factor of a thousand.

A kilojoule (kJ) is the SI unit. One kcal is 4.184 kJ.

The useful mental shortcut: divide kJ by 4 to get roughly kcal, or multiply kcal by 4 for roughly kJ. That is about 4% out, which is well inside the tolerance labels are allowed anyway.

Who uses which

EU and UK: both are mandatory, kJ first then kcal. Front-of-pack traffic-light labelling shows kcal.

Australia and New Zealand: kJ is the primary and often only unit, which is why the "8,700 kJ" daily figure is so widely recognised there and meaningless elsewhere.

United States and Canada: kcal only, printed as "Calories" with a capital C.

This scanner shows both regardless of where the product came from. Where a record carries only kJ — common on European products — we convert at 4.184 and label it as converted rather than passing it off as a declared value.

Per 100 g and the metric convention

EU and UK labels must declare per 100 g or per 100 ml, with per-portion figures optional alongside. This is genuinely useful for comparing two products directly, and genuinely unhelpful for working out what you are about to eat, since nobody's portion is exactly 100 g.

The scanner defaults to the manufacturer's stated serving where one exists and lets you set any weight you like, with every figure updating live. Both views are one tap apart.

One difference worth knowing about carbohydrate

EU and UK labels declare carbohydrate excluding fibre, which is listed separately. US labels declare total carbohydrate including fibre. The identical food therefore shows a higher carbohydrate figure on a US label than a European one, with neither being wrong.

This is where "net carbs" comes from — it is a US concept for arriving at the number a European label already gives you directly. If you are following a plan written for one market using labels from the other, this is the discrepancy that will confuse you.

Salt versus sodium

UK and EU labels declare salt in grams. US labels declare sodium in milligrams. Salt equals sodium multiplied by 2.5, so 1 g of salt is 400 mg of sodium. The scanner shows sodium in mg and converts from salt where that is all the record holds, noting when it has done so.

Scan a label and read it in whichever unit you think in.